The present invention relates to a method of cleaning a surface of a substrate using 1-chloro-3,3,3-trifluoropropane as a solvent.
Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room-temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the act. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancilliary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents.
Fluorocarbon solvents, such as trichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like. Trichlorotrifluoroethane has two isomers: 1,1,2-trichloro-1,2,2- trifluoroethane (known in the art as CFC-113) and 1,1,1-trichloro-2,2,2-trifluoroethane (known in the art as CFC-113a).
Chlorofluorocarbons (CFC) such as 113 are suspected of causing environmental problems in connection with the ozone layer. In August 1988, the U.S. Environmental Protection Agency issued its final rules ordering a freeze on CFC production including CFC-113 at 1986 levels by mid-1989. Additional 20% and 50% cuts in CFC production are scheduled for 1993 and 1998.
In response to the need for stratospherically safe materials, substitutes have been developed and continue to be developed. Research Disclosure 14623 (June 1978) reports that 1,1-dichloro-2,2,2-trifluoroethane (known in the art as HCFC-123) is a useful solvent for degreasing and defluxing substrates. In the EPA "Findings of the Chlorofluorocarbon Chemical Substitutes International Committee", EPA-600/9-88-009 (April 1988 , it was reported on pages C-22 and C-23 that HCFC-123 and 1-fluoro-1,1-dichloroethane (known in the art as HCFC-141b) have potential as replacements for CFC-113 as cleaning agents.
Commonly assigned U.S. Pat. No. 4,947,881 teaches a method of cleaning using hydrochlorofluoropropanes having 2 chlorine atoms and a difluoromethylene group. European Publication 347,924 published Dec. 27, 1989 teaches hydrochlorofluoropropanes having a difluoromethylene group. International Publication Number WO 90/08814 published Aug. 9, 1990 teaches azeotropes having at least one hydrochlorofluoropropane having a difluoromethylene group.
A wide variety of consumer parts is produced on an annual basis in the United States and abroad. Many of these parts have to be cleaned during various manufacturing stages in order to remove undesirable contaminants. These parts are produced in large quantities and as a result, substantial quantities of solvents are used to clean them. It is apparent that the solvent used must be compatible with the material to be cleaned.
Solvents should be stabilized against possible changes during storage and use. One problem with CFC-113 is that it hydrolyzes to form HCl. When metallic materials are present such as occurs in many cleaning applications, the problem is worsened because the metal acts as a catalyst and causes the hydrolysis of CFC-113 to increase exponentially. Metallic materials such as Al-2024, copper, cold rolled steel, galvanized steel, and zinc are commonly used in cleaning apparatus. Another potential change is due to ultraviolet light decomposing CFC-113. This hydrolysis problem also occurs with hydrochlorofluorocarbon solvents such as 1,1-dichloro-2,2,2-trifluoroethane (known in the art as HCFC-123) because chlorine and hydrogen atoms are on the same carbon or adjacent carbons.
It is an object of the invention to provide a novel solvent for cleaning substrates.
It is another object of the invention to provide such a novel solvent which is stratospherically safer than currently used solvents.